(1) Field of the Invention
The present invention pertains to the field of hot metal processing equipment and a method of using such equipment, for instance when making steel and iron.
(2) Background Art
The present invention relates to removal of impurities from a quantity of molten hot metal in a ladle during ironmaking, or alternatively, during steelmaking, as both processes use similar equipment and methods. References to steelmaking hence are also applicable to ironmaking and the use of the term “steelmaking” here is meant to include ironmaking as well. Slag is a term of art in the steelmaking industry referring to waste impurities produced when a desired metal has been separated from its raw ore, and typically floats to the surface of the molten metal. The impurities are skimmed off the surface of the molten or hot metal before the metal is sent for processing. Presence of impurities affects the quality and characteristics of the finished products, consolidating and efficiently removing impurities reduces production costs, and improves yield and metal quality.
Currently, steelmakers use two methods to separate waste or impurities from hot metal: (1) material methods that introduce desulfurizing agents deep into the hot metal to chemically bind the sulfur for easier removal, and (2) stirring methods that physically stir the hot metal by creating turbulence to agitate the body of metal so as to allow better distribution of desulfurizing agents and thus allow the desulfurizing agents to work more efficiently.
For material methods, material (desulfurizing agents) are commonly delivered into the hot metal via a typical “straight” through lance, one of many configurations of lances used in steelmaking, the lance consisting of a pipe with the majority of the length coated with a refractory material. The purpose of the refractory coating is to prevent the pipe from melting or distorting while submerged in the hot (molten) metal. This type of lance simply delivers the injected material to the bottom of the ladle with a minimum amount of stirring of the material into the hot metal. The only stirring gas available is provided by the gas which conveys the material into the ladle and/or the vaporization material.
A known issue with material methods using lances is the lack of uniform dispersion of material into the hot metal. The reagent is only present in sufficient quantities in around the lance itself, the result is a decreased effectiveness in removing sulfur impurities from the entire body of hot metal.
Regarding the material and stirring methods, the prior art teaches that use of the stirring method is optional when using a material injection method, although steelmakers often use the stirring method in conjunction with the material method as this typically results in better mixing of reagent and thus increased removal of impurities from the hot metal.
Another type of material lance design is a “T” lance, in which the bottom of the main pipe is shaped like an inverted letter “T” so as to move the material away from the lance in two different directions. This process is an improvement over the other lance style since it moves the material away from the lance and thus improves distribution of the material to a degree.
For stirring methods, a rotary lance has been developed to physically stir the hot metal, by rotating the lance while submerged in the hot metal via a motor and speed reducer system. The main drawback to this system is that it must be installed above a lance drive, which requires the lance drive to be of a substantial structure to be able to support the additional weight of the machinery needed to rotate the lance.
The prior art teaches the use of both material and stirring methods together, as well as separately, however in reality, most steelmakers are forced by economic reasons to use only one method as the capital investments required for both methods is often cost prohibitive. For instance, a highly effective material-stirring lance is described in U.S. Pat. No. 9,259,780 B2 (Waitlevertch et al.) granted 16 Feb. 2016, for which the present inventor is also a co-inventor, but the main drawback of this system is the need for costly modifications to existing equipment in order to support the weight of the machinery required to rotate the lance, again adding to capital costs, and downtime to do such modifications.
What is needed is an improved lance that increases efficiency and requires no significant nor expensive investments or modification to existing equipment, and is cost effective to steelmakers.